The formation of metal components in various desired sizes and shapes using molds is an extensively developed art in which numerous prior art techniques, methods, and mold constructions have been developed. Within this prior art technology is the extensive effort that has been expended in the field of investment casting wherein molds are formed to the precise size and shape of the desired component and then sacrificed after formation of the product therein.
Throughout the years, investment castings have been used extensively due to the unlimited flexibility of the overall casting design. In particular, investment casting has become extremely popular for complicated components which would otherwise require numerous operations to manufacture or numerous separate components to achieve. In addition, metals or alloys can be employed in investment casting which are otherwise incapable of being effectively manufactured. Furthermore, extremely tight tolerances can be maintained and improved physical properties realized from the resulting metal component.
In general, two basic techniques are employed in producing cast products using the investment casting process. These two methods are known as the investment flask casting process and the investment shell casting process. In either process, a mold is made for the component to be manufactured with this mold being constructed with great precision and close tolerances. However, since this mold is employed only for making wax or plastic components, a soft metal, such as aluminum, is typically used, thereby enabling a precision mold to be manufactured at a reasonable cost. Then, using this mold, a plurality of the wax or plastic components are manufactured.
In the next step, the plurality of wax or plastic components are mounted to a central sprue or a plurality of sprue-forming members by elongated wax or plastic members, such as rods or tubes, which form the gates or runners through which the metal will flow to reach the component casting. The pattern resulting from this operation depends upon the size and shape of the components being manufactured, as well as the flow pattern for the molten metal.
Once the pattern has been established, the actual investment casting is manufactured in either the flask casting technique or the shell casting technique. Both of these techniques are well known in the art and have been successfully employed for many years. Regardless of which technique is used, the mold or shell created possesses a central sprue or a plurality of sprues, into which the molten metal is poured, for being delivered to the gates or runners which carry the metal to the casting or void zone, which have been created in the precise size and shape of the desired product.
More recently, investment casting shells have been manufactured using computer technology. In this system, an investment casting shell is produced, layer by layer, at the micron level. However, regardless of the method of production employed, the resulting casting is substantially identical and suffer from the same drawbacks.
One of the problems encountered occurs in the actual forming of the components by pouring the molten metal into the feed mechanism of the investment casting. Typically, gravity feed is most commonly used, however, if desired, the investment casting may be filled with the molten metal employing pressure, vacuum, or centrifugal force. Since the use of pressure, reduced pressure, vacuum, or centrifugal force requires a more complicated and expensive manufacturing operation, investment casting is most often filled by employing gravity feed. Although this operation has proven to be extremely effective in providing high quality components, several drawbacks do exist and have been incapable of being eliminated.
One of the principal drawbacks is slag or oxides which are formed in the molten metal and are present on the surface of the molten metal as the metal is being poured into the investment casting. Since these impurities are usually found on the top surface of the molten metal, these impurities are the first to enter the investment casting as the molten metal is poured into the casting. Although filters have been used, these filters are unable to completely eliminate these impurities, while also controlling the flow under head pressure required. As a result, these impurities are retained in the metal flow and are often trapped in some of the components produced, thereby degrading the quality of those components.
In addition, as the molten metal is poured into the feeding mechanism of the investment casting, a turbulent flow is created, causing air to be retained in the metal flow and be incorporated into the metal. The air remains with the metal as it flows through the investment casting, creating flaws in the components produced. This turbulence problem is of particular concern in all metals in general and in skin forming alloys, in particular, which are sensitive to turbulence.
Another problem often encountered with investment castings is the control of the flow to assure complete filling of the entire casting in a manner which will produce uniformly dense, structurally sound components. Although the casting is designed with metal flow as one of the controlling factors, accurately predicting the metal flow throughout the mold is difficult and often not achieved.
Prior art attempts have been made to overcome some of the drawbacks discussed above. In this regard, it has been found that by feeding the investment casting from the bottom, instead of from the top as most usually done, a more uniform flow pattern is achieved and some of the difficulties encountered with top feeding are eliminated. However, in order to achieve bottom feeding, a secondary feed column or sprue must be formed which is connected to the base of the central sprue. Although this is effective in providing bottom feeding to the casting, substantially more molten metal is required, which substantially increases the cost of manufacturing. In addition, with components wherein the metal employed is extremely expensive, the bottom feeding technique might not be employed due to the added expense for the expended material.
Therefore it is a principal object of the present invention to provide a feed system and method of use for investment castings which provides the benefits of bottom feeding while also reducing the amount of material needed to fill the casting.
Another object of the present invention is to provide a feed system and method of use for investment castings having the characteristic features described above which is easily employed without altering the methods used for creating the investment casting or altering the metal filling process used therewith.
Another object of the present invention is to provide a feed system and method of use for employing investment castings having the characteristic features described above which is capable of eliminating the incorporation of any trap slag or oxides in the components being manufactured.
A further object of the present invention is to provide a feed system and method of use for investment castings having the characteristic features described above which eliminates turbulent flow, thereby eliminating air entrapment within the molten metal and resultant components.
Another object of the present invention is to provide a feed system and method of use for investment castings having the characteristic features described above which assures complete filling of the entire casting while also producing a higher quality product.
Other and more specific objects will in part be obvious and will in part appear hereinafter.